Alternative Strategies for Hypoxia Management

The Long Island Sound Comprehensive Conservation and Management Plan (CCMP) identifies low dissolved oxygen, or hypoxia, as the most serious water quality impairment in the Sound. The annual summertime occurrence of hypoxia in the deeper waters of western Long Island Sound reduces the amount of healthy habitat necessary to support fish and shellfish. The CCMP identifies excessive discharges of nitrogen, a nutrient, as the primary cause of hypoxia, and sewage treatment plants as the primary source of this excess nitrogen. To address this problem, the Long Island Sound Study (LISS) is implementing a phased approach to reducing nitrogen loads to the Sound from sewage treatment plants, industrial dischargers, and nonpoint sources.

These phased nitrogen reductions, however, may not raise dissolved oxygen to levels necessary to support all life stages of marine life in Long Island Sound. Additional measures will likely be required to achieve the states’ water quality standards for dissolved oxygen. These measures may include advanced treatment at sewage treatment plants upstream of the Connecticut border, reductions in atmospheric nitrogen loadings, and several “nontreatment” techniques, which are the subject of this fact sheet.